This invention claims priority of a German patent application DE 100 07 650.5-33 which is incorporated by reference herein.
1. Field of the Invention
The invention concerns a microscope having an electron beam for illumination. In particular, the invention concerns an electron microscope that is similar in its configuration to a conventional microscope. The objectives are arranged on a revolving nosepiece so that the objective having the desired magnification can be pivoted into the beam path.
2. Background of the Invention
The article entitled xe2x80x9cElectron beam microcolumnxe2x80x9d by T. H. P. Chang et al. which appeared in Microelectronic Engineering 32 (1996), pp. 113-130, underlines the importance of scanning electron microscopy at low voltages. Applications exist in surface inspection, metrology, and lithography. Electron-optical columns are manufactured using the micropatterning technique, and are multiple-layer systems made up of layers having different electrical properties. The electron-optical columns produced in this fashion are operated at a voltage of approx. 1 keV.
Scanning electron microscopy is known and extensively developed. The resolution of scanning electron microscopy exceeds the resolution of optical systems by several orders of magnitude: a resolution of a few nanometers can easily be achieved with it. U.S. Pat. No. 5,828,064 discloses an electron microscope with which samples can be examined in a chamber provided especially for the purpose. The gas pressure in the chamber is kept at between 10xe2x88x922 and 50 torr. The configuration of the electron microscope comprises at least four different vacuum zones that create a pressure difference of 10xe2x88x9210 torr between the electron gun and the sample chamber. The various pressure regions are created in the electron-optical column that is placed on the sample chamber. A rapid and convenient change in magnification is not, however, possible with this system. In addition, the configuration of a scanning electron microscope of this kind is large, expensive, and difficult to manipulate.
It is the object of the present invention to create a microscope that achieves the resolution of conventional scanning electron microscopes and possesses an economical configuration. The microscope should differ very little from the overall size of conventional light microscopes.
This object is achieved by a microscope which is characterized in that at least one objective that can be arranged in the optical axis is configured as an electron beam objective.
One advantage of the invention is that in one specific embodiment, the samples can be examined under standard environmental conditions. The electron beam objectives used are comparable, in terms of their size, to the objectives of conventional light microscopes. This miniaturization is made possible by advances in micropatterning technology, and in this case in particular by silicon processing technologies. A further advantage of the invention is that electrostatic charging of the samples is avoided. This is due on the one hand to the fact that the electron beam is generated in the electron beam objectives using low acceleration voltages (on the order of 1 keV). On the other hand, ambient air is ionized at the transition from the electron beam objective to the sample, thus making it possible to dissipate the charge. A microscope according to the invention can be configured in particularly versatile fashion. For example, the electron beam objectives can be mounted on a revolving nosepiece, allowing a rapid changeover between different magnifications. Moreover, an optical objective can be provided in addition to the electron beam objectives, making possible, in the working position, purely optical observation of the sample at a lower resolution. Since the microscope can also be used for purely optical imaging, an optical unit which defines an optical axis is provided. An electron beam objective can be arranged in alignment with the optical axis, e.g. can be introduced by way of the revolving nosepiece into the optical axis and into the so-called working position. In the working position, the electron beam objective, comprising an electron microscope column, is arranged symmetrically about the optical axis. For many applications, it is particularly advantageous if the electron beam objective is spaced slightly away from the surface of a sample being examined. The samples can thus be examined under standard environmental conditions, thereby eliminating any complex preparation or even damage. The electron beam objective can thus be arranged in such a way that standard air pressure is present between the sample and the electron beam objective. In one possible configuration of an electron beam objective, it comprises a first housing that encloses a second housing. The electron microscope column is arranged in the second housing, symmetrically about the optical axis. Also provided are appropriate vacuum devices which maintain in the first housing a lower air pressure than in the external environment. In the second housing, a vacuum is created that is even more greatly improved as compared to the first housing.